Preferred solution, K12

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0 15.08.2019 Final issue HPO ANE SEJ Rev. Publish

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Document name:

Preferred solution, K12 – Appendix L Design of cable stayed bridge and abutments

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SBJ-33-C5-AMC-22-RE-112

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Ferry free E39 –Fjord crossings Bjørnafjorden 304624

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CONCEPT DEVELOPMENT, FLOATING BRIDGE E39 BJØRNAFJORDEN

Appendix L – Design of cable stayed bridge and abutments

CLIENT

Statens vegvesen

DATE: / REVISION: 15.08.2019 / 0

DOCUMENT CODE: SBJ-33-C5-AMC-22-RE-112

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REPORT

PROJECT Concept development, floating bridge

E39 Bjørnafjorden DOCUMENT CODE SBJ-33-C5-AMC-22-RE-112

SUBJECT Appendix L – Design of cable stayed bridge and

abutments – K12 ACCESSIBILITY Restricted

CLIENT Statens vegvesen PROJECT MANAGER Svein Erik Jakobsen

CONTACT Øyvind Kongsvik Nedrebø PREPARED BY

Henrik Polk / Arne Munz / Tore B. Aas / Torben Forsberg / Petter Buckholm

RESPONSIBLE UNIT AMC

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Concept development, floating bridge E39 Bjørnafjorden

Appendix L – Design of cable stayed bridge and abutments 1 Cable stayed bridge

SUMMARY

Introduction: The cable stayed bridge is constituting the south portion of the Bjørnafjorden Bridge, "cantilevering"

from Reksteren across the Svarvahelleholmen Island and connecting to the floating bridge at axis 3. The tower is positioned on the island, while the 380 m main span allows the navigation to pass under at a height of 45 m and a width of 250 m or more.

Concept for cable stayed bridge and south abutment: The bridge spans from the south abutment to the tower are 40 + 4 x 55 + 140 = 400 m. This span arrangement and the corresponding cable stay configuration (380 m main span/250 m side span/18 stays/4 fans) is the result of an evaluation of feasible cable stayed bridge options that fit with the general scheme of the floating bridge.

Of the 380 m long main span, 360 m belongs to the cable stayed bridge, whereas the remaining 20 m is part of the floating bridge. With the 140 m side span there is totally 500 m closed steel box bridge deck. The remainder of the bridge deck, 110m cable stayed side span and three viaducts spans, all together 260 m, is a closed concrete box structure. The tower, piers and abutment are all concrete structures. The bridge superstructure is integrated with the abutment and the piers, whereas bearings are supporting the steel deck vertically and laterally at the tower, allowing relative longitudinal movements of the deck. Thermal contraction/expansion of the viaduct spans results in flexure of the piers. There are no expansion joints in the bridge deck, neither at the abutment, at the tower nor at the

intersection to the floating bridge. Axial compression forces in the bridge deck caused by stay inclinations are in balance about the tower, whereas other axial loads are transmitted through the cable stayed bridge and into the abutment. All in all, the cable stayed bridge consists of well-known standard solutions built before and therefore not adding significant risks to the project.

At the tower section of the bridge deck, the ULS strong axis bending moment becomes 2100 MNm. The ALS ship collisions to the pontoons or deck house impacts to the floating bridge deck structure lead to maximum moment of 3300 MNm. The ship collision impact and ULS load combinations lead to high lateral loads to the side span piers. The pier nearest to the tower is thus subjected to a high shear force and a consistent overturning moment.

Concept for north abutment: At the north end of the floating bridge, a huge concrete abutment ties the bridge to the Gulholmane Island. There is no expansion joint at this end either, and the structure is subjected to high axial loads in combination with very high bending moments due to transverse wind and wave loads to the floating bridge. The governing maximum ULS bending moment becomes 2400 MNm. The governing moment in the ALS ship collision situations becomes 5900 MNm. Both ship collisions to the pontoons or deck house impacts to the floating bridge deck structure are critical and the above results are based on refined ship collision analyses. To resist the ship collision forces transferred into the abutment the fill inside the abutment is iron ore.

Steel deck: The bridge deck is steel grade S420. The closed steel box is subjected to load effects comparable with those of the floating bridge. Therefore, it is natural that the design of the cable stayed steel deck follows the design concepts of the floating bridge deck of a closed steel box with a traditional orthotropic deck, circumferential skirt plates with trough/bulb stiffeners. Truss-type transverse diaphragms stabilise the longitudinal plates of the box girder, and tubes are slotted through the edges for cable stay anchorages. The standard (minimum) cross section properties will provide enough strength except at the tower region and when approaching the first floating bridge pier A3, where ULS and ALS ship collision loads require some reinforcement of the structure. The linear weight of the steel structure is in average 17.0 tonnes/m, totally 8500 tonnes.

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Concrete deck: The closed 4-cell concrete deck that constitutes the three viaduct spans and the two stayed spans has ample reserves to cater for the various load effects, thus a moderate amount of posttensioning will be sufficient. The stay anchorage tubes are cast with the concrete and the passive end of the cables are sticking through the bottom.

Tower: The tower has a distinct A-shape which provides transverse strength and stiffness to the bridge and enables it to transfer very high horizontal forces to the ground. The ground quality is good, hence relatively small foundation slabs are required. The lower part of the concrete legs is very robust, and with the cross beam they constitute a very strong frame in transverse direction. With the present geometry, the frame can resist transverse load of 50 MN, while the actual load becomes 35 MN transmitted through the bearing on the side of the deck when a ship collides with the pontoon in axis 3. This load case together with the ULS load situations governs the lower part of the tower for loads in transverse direction. Wind on free standing tower in longitudinal direction governs the capacity in that direction.

Otherwise, the various section verification will be straight forwards and moderate amounts of reinforcement will be required for the tower to resist the demands. The cross beam will have longitudinal posttensioning cables, and some vertical cables shall be cast in the inner flange of the lower leg for strengthening of the frame corner. The tower legs above deck level are slender and the compartment for the stay anchors are thus compact. However, they are large enough to allow for stay stressing equipment during construction. The stay anchors are fixed to internal steel boxes that work with the tower concrete structure by means of shear connectors. The steel boxes provide the necessary tie between the horizontal component of the stay force on either side of the leg, whereas the shear connectors transfer the vertical load component to the tower leg.

Cable stays: The stays are parallel multi-strand cables. The stays nearest the tower have 31 strands, and the longest stays have 67 strands. The stays are constructed by strand-by-strand tensioning. The strands are PE-sheathed individually and enclosed in HDPE-pipes. The cables have anchorages that fit with steel tubes integrated with the main structure at either end. The wire strength is 1860 MPa, and the total weight is approximately 1000 tonnes. The cable size is driven by ULS1 (permanent load dominant) and ULS2 (traffic load dominant) combinations, whereas ULS3 (wind and wave dominant) is slightly less demanding. The ship collision case is not critical. The outermost stays towards the first floating bridge pontoon have been fatigue checked without being found critical.

Piers: The piers are 10–11 m wide and 2–2.5 m thick and stand on simple rectangular foundations. The height varies in accordance with the topography, the tallest will be about 56 m high. The piers will be governed by both the ship collision effects and ULS3 combination. For the tallest pier in axis 1-E, wind on free standing pier is critical for the size of the foundation and for the reinforcement in bottom of the pier.

South abutment: With piers integrated with the bridge deck, the south abutment is not subjected to high forces from ship collision, as was the case for the previous phase concepts. The abutment can therefore be designed for the longitudinal axial force in the bridge deck. The force requires a gravity construction that can resist the longitudinal force by means of friction. The abutment is a cell concrete structure 30 m long and 28 m wide and a height of 9.5 m filled with gravel.

North abutment: The north abutment is highly determined by the large horizontal bending moments from ship impact (bridge girder strong axis moment). Similar high moments occur also for normal wind and wave loads, but not quite as severe. It has been found necessary to design a concrete cell structure which is large enough to contain enough ballast to prevent rotation by means of friction between the base and ground. The north abutment becomes 50 m long and 36 m wide and 10.0 m high. With the present high ship collision loads it is found beneficial to use iron ore as ballast material within the abutment. The bridge deck adjacent to the north abutment is widened and has increased strength compared with normal sections of the floating bridge. The joint between the abutment concrete structure and the steel deck is secured with longitudinal posttensioning cables.

Construction works: Some of the construction works for the cable stayed bridge is done in prefabrication yards, but most of the work is carried out at site. The cable stays, steel anchor boxes and deck sections are prefab elements that are brought to the construction site for installation. The in-situ works begins with establishment of the work site and access roads. The tower construction will be on the critical time path, so the works must start early by blasting and preparation for the in-situ concreting of the foundation slabs. After casting of slabs, the lower legs can be constructed by use of jump forms. Due to the inward inclination of legs, temporary propping will be required to prevent high

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Concept development, floating bridge E39 Bjørnafjorden

Appendix L – Design of cable stayed bridge and abutments 1 Cable stayed bridge

Alternative bridge deck layout: The selected concept doesn't necessarily show the fully optimal solution for the cable stayed bridge. An alternative concept has therefore been considered if longer side- and viaduct spans will be feasible utilising the natural strength of the 3.5 m deep concrete deck box structure, thereby save one pier and improve architecture with a shorter side span in combination with an equal stay spacing. The concrete deck might also be extended to the tower and further say 40 m into the main span with cost saving as a result. This option might be possible as the ALS ship collision forces have stabilised at a moment of approximately 3300 MNm, which the concrete box structure can easily resist. The development of the cable stayed bridge is presented below as "alternative layout".

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1 Cable stayed bridge

1.1 Concept layout - general arrangement

The cable stayed bridge is constituting the south portion of the Bjørnafjorden Bridge, "cantilevering"

from Reksteren across the Svarvahelleholmen Island and connecting to the floating bridge at axis 3.

The tower is positioned on the island, while the 380 m main span allows the navigation to pass under at a height of 45 m and a width of 250 m and even some 20 m more. The bridge spans from the south abutment to the tower are 40 + 4 x 55 + 140 = 400 m. This span arrangement and the corresponding cable stay configuration (380 m main span/250 m side span/18 stays/4 fans) is the result of an evaluation of feasible cable stayed bridge options that would fit with the general scheme of the floating bridge, see below Figure 1-1. This is the concept selected and incorporated in the overall floating bridge analyses, belonging FE-modelling, drawings, bill of quantities etc.

Figure 1-1 Cable stayed bridge – concept layout

The width of the bridge deck basically follows the shape of the floating bridge but is widened to give space for the cable stay anchorages. The stays anchorages are 28.0 m apart with a spacing along the bridge girder of 20.0 m for steel respectively 10.0 m for concrete. Along the tower the vertical spacing between the anchorages is chosen to 5.0 m.

The stayed span lengths lead to an asymmetrical bridge which becomes natural as piers can be erected on shore in the side span supporting the deck girder and moreover giving stiffness to the entire cable stayed bridge. The bridge deck is in principle divided into a steel portion above water, and concrete above land continuing with the concrete viaduct spans.

The cable stayed bridge is of a fully conventional type, and the most significant influence from the floating bridge is in general tidal variation and to some extent wave motion of pontoon at axis 3.

These none common loading events leading to dynamic stay forces and bending of the steel deck have been examined carefully without giving significant impact to the design. The distance from the last stay cable to the first pontoon of the floating bridge is selected to 20 m but a parameter which can be furthermore fine-tuned later. The most severe impact from the floating bridge is for sure the ship collision to the bridge deck and the first pontoon of the floating bridge, which however is fully common design situations for cable stayed bridges.

The bridge deck and tower have a tight fit in transverse direction where the deck is supported on normal sliding bearings to the tower legs. The tower is a strong point being able to accommodate the

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transverse loading from ship collision and normal ULS load situations, see furthermore the tower description in section 1.4. In vertical direction the deck is supported by normal bridge bearings on the tower cross beam and in the longitudinal direction the deck is free to move. In general, the aim has been to avoid bridge bearings and expansion joints and it has therefore been investigated if the bridge deck and tower structure could be monolithically connected. This showed however up not being feasible as temperature loading within the 400 m long concrete deck (side span and viaduct) will govern the tower design.

However, the viaduct is monolithic with the abutment and piers and further integrated with the concrete bridge deck. For ship collision the piers are therefore designed to accommodate the high transverse loads.

The entire cable stayed bridge has a straight horizontal alignment and a visualisation of the bridge can be seen below in Figure 1-2.

Figure 1-2 Cable stayed bridge - visualisation

1.2 Alternative layout of bridge deck

The above concept is not necessarily a fully optimised solution in all aspects and it does not fully reflect all architectural preferences. An alternative concept is therefore presented in Figure 1-3.

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Here it has been considered if longer side- and viaduct spans up to 72 m might be feasible utilising the fully natural strength of the 3.5 m deep concrete deck box structure and thereby save one pier and give an architectural improvement to the project. The concrete box girder is furthermore extended to the entire side span and further say 40 m into the main span with the aim reducing the cost and improve the bridge appearance of having an equally stay spacing throughout the entire side span. The alternative layout perhaps becomes even more feasible now as the ALS ship collision forces at tower section tending to stabilise at a maximum bending moment of 3300 MNm.

1.3 Analyses

The analyses supporting the cable stayed bridge (and abutment) design are combinations from different analyses:

 global, dynamic wind and wave analyses of floating bridge (ORCAFLEX)

 global dynamic analyses of ship collision to floating bridge (LS-DYNA)

 permanent load, temperature and traffic (RM Bridge)

 a local dynamic wind analysis of critical construction stages for the cable stayed bridge (Novaframe analysis described in this appendix)

 local cable stayed bridge (SOFISTIK, described in this appendix)

The various results are found accurate enough to justify the technical feasibility and the quantities of the cable stayed bridge and abutments.

The design of the cable stayed bridge will predominantly be controlled by ULS (both construction stages and permanent stage) and ALS ship collision demands. However, SLS might also governs the design of some tower- and pier elements. At this stage, mainly the ULS and ALS cases have been verified, which for the ULS combinations are:

 ULS 1 permanent load dominant

 ULS 2 traffic load dominant

 ULS 3 environmental load dominant

 ULS wind analysis of different construction stages

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1.4 Tower

The tower has a distinct A-shape that is

architecturally preferred, and which is optimal seen in relation to the demanding ship collision loads being able to accommodate large forces in the transverse direction.

The tower is a concrete structure 220 m tall and A- shaped, meaning it has a high transverse stiffness and strength. The tower will also act strong for uneven loading of the cable planes in traffic and ship collision situations due to the interconnection of the legs at the top. The lower legs and cross beams are strong and forms a frame able to transfer large horizontal loads from ship impact to the ground. The form is technically sound and aligns well with the architect's preference, see Figure 1-4.

The lower legs taper towards the foundation, where the bending moments therefore become small, hence the leg sections need to be large where they meet the cross beams. Due to esthetical reason the tower foundations are selected fully buried into the ground.

The analyses show that ship collisions and ULS tower demands are almost equally important.

The concrete volumes at the cross beam connection to the leg are quite substantial and will occupy some space inside the tower. The frame connection requires transverse posttension from outside leg to outside leg through the cross beam, and likely also vertical posttensioning some depth down the inner flange of the lower leg.

Above the bridge deck, the tower legs are slender due to aesthetic reasons meaning that the compartment becomes compact. Moreover, the anchorages have been placed asymmetric in the legs making it possible to position all the stay anchorages along a straight line meeting each other at the tower top. At the location of steel boxes for the cable stay anchorages, there is only limited space for a stair to pass on one side of the asymmetrical placed stay

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Due to esthetical reason the tower stay anchorages are spaced every 5.0 m, which is more than normal, i.e. it will be easy to adopt the cable stay forces in the steel anchor structure and transfer it to the concrete by means of shear connectors. This will furthermore make the stay tensioning within the tower easier.

Figure 1-5 Tower – plan section through leg at stay anchorages At the tower top, the two legs are merged and taper further towards the top. Here the space

conditions will be constrained to keep the slender impression. Normal concrete strength C40 – C50 will suffice, and the reinforcement quantity will be normal, 150 – 200 kg/m³.

The concrete tower structure of the cable stayed bridge can be seen to be well documented standard products built before and therefore not adding significant risks to the project.

A visualisation of the cable stayed bridge can be seen in Figure 1-6 where the tower forms almost a lighthouse landmark.

Figure 1-6 Cable stayed bridge with the tower forming a light house landmark

1.5 Bridge deck

1.5.1 Bridge deck – steel

For the selected concept, the steel bridge deck starts 140 m from the tower into the side span and continues throughout the entire main span of 380 m until 20 m from the first pontoon pier A3, see also Figure 1-1. The length of the steel deck then becomes 500 m with an average total girder weight of 17.0 t/m. The steel deck is much lighter than the concrete deck and therefore a natural choice for the main span. In the side span the steel deck has been chosen going 140 m into the span due to high bending moments round strong axis from ship impact in the tower region and furthermore to span over the water to the first pier A1E.

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An alternative layout of the bridge deck has already been mentioned and described briefly in section 1.2 considering extending the concrete girder to the entire length of the side span in the aim of optimising the design further. This option has become possible as the ship collision forces have decreased reaching a maximum level of 3300 MNm round strong axis at tower position.

A cross section of the bridge girder can be seen in Figure 1-7 where the steel girder is optimised for the cable stayed bridge having a reduced girder depth of 3.5 m instead of 4.0 m as for the floating bridge. The cross section is more aerodynamically shaped with wind noses and wider to

accommodate the cable anchorages. A wider deck is also beneficial withstanding the large moments round strong axis from ALS ship collision as well as normal ULS. The outer vertical web plate from the floating bridge spaced 27.0 m can be found unchanged in the cross section layout for the cable stay bridge, now supporting the stay anchorages.

Figure 1-7 Steel bridge girder – cross section, longitudinal steel

The deck plate varies from a minimum thickness of 16 mm up to 20 mm when approaching the tower from both side- and main span and again when approaching the first floating bridge pier 3. Fatigue calculations carried out documents that a deck plate of min 16 mm will be necessary instead of the more conventional 14 mm due to truck loading. The trapezoidal stiffeners underneath the deck plate vary from minimum 8 to 10 mm, again to accommodate the fatigue requirements.

The bottom plate and the inclined web plates varies from a minimum thickness of 12 mm up to 20 mm near the tower and again when approaching the first floating bridge pier 3. For the bottom plate the principles using bulb stiffeners are chosen due to preference of the floating bridge.

The cross section layout is further described in section 3.3.1. and Figure 1-8 shows the layout of the transverse truss diaphragm with a spacing in the bridge line of 4.0 m. The transverse truss solution has been selected as it in general is lighter than a full plated diaphragm solution.

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The deck constitutes an important part of the cable stayed bridge which is a well-documented standard product not adding a significant risk to the project. The steel girder quantity becomes 8600 t equal to an average total girder weight of 17.0 t/m. The steel bridge deck constitutes 40-45% of the total bridge cost.

1.5.2 Bridge deck – concrete

The concrete bridge deck is fully fixed in the abutment and to the steel deck. The total length for the concrete deck is 260 m. In the distance of 110 m closest to the tower, stay cables are anchored in the cross section. The distance between the stay cable planes is chosen to be 28.0 m. The width of the cross section is therefore selected to 29.5 m giving sufficient space for the stay cable anchorages.

It is possible to reduce the cross section width between the abutment and the cable stayed bridge.

However, this will also be an aesthetically evaluation.

The cross section height is 3.5 m, somewhat optimal for a span length of 55 m and upwards. The thickness of the bottom slab is 280 mm while the top slab is 300 mm and web thicknesses are 450 mm. Diaphragms are used at each pier and at each stay cable anchor. The diaphragm thickness is 3000 mm at piers and 500 mm at stay cable anchorages. 24 prestressing tendons with breaking load 5300 kN are used above the piers and 12 prestressing tendons within the field. Normal

reinforcement amount of 160 kg/m³ concrete is used. A cross section of the box girder can be seen in Figure 1-9.

A wide box section type is chosen due to the following reasons:

 The cross section shape is similar to the cross section layout within the main span

 Forces from the stay cables can easily be incorporated in the cross section

 The bridge deck is subjected to high bending moment about strong axis from ship collision which becomes favourable having large concrete areas close to the outer edges of the cross section

 Small reinforcement amount is needed in the transverse direction due to the cross section shape Construction of the bridge girder for the selected concept can e.g. be done by:

 Use of MSS (movable scaffolding system, spanning from pier to pier) for concrete cross section typical max 70-75 m between piers/temporary supports

 Incremental launching (ILM) with typical max 50-55 m between piers/temporary supports

 Concrete cast in place with scaffolding supported on ground

Figure 1-9 Concrete box girder - cross section

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The concrete girder of the cable stayed bridge can be seen to consist of well documented standard products not adding significant risks to the project.

1.5.3 Bridge girder joint

The joint between the steel bridge girder and the concrete girder is located 135 m from the tower near the first side span pier. Here the strong axis bending moment due to ship collision is reduced to 50% of the maximum moment at the tower or less and the connection by means of post-tensioning cables and high-strength bars will then be less demanding.

The joint will be based on the same principles as used for the Pont de Normandie (France). The posttensioning cables will be anchored a certain distance from the joint inside the steel box and be cast in the concrete deck. Along the circumference of the steel box a number of high strength bars will be installed at tight spacings.

The connection could be established in two steps. First the steel box and the concrete deck is brought near to each other and partially stressed. In this locked situation a stich joint concrete (grout) is cast ensuring the complete connection of the two bridge deck types. After curing of the stich joint, the cables and bars are fully tensioned.

The bridge girder joint of the cable stayed bridge is not a standard solution within cable stayed bridges but is however well-known technology from other large cable stayed bridges as the Pont de Normandie in France and the Russky Bridge in Russia, both well known within the Joint Venture. The joint will therefore not add any significant risks to the project.

1.6 Cable stays

The cable stays of the bridge are multi-strand type with 31–67 no of strands, each 15.7 mm dia.

having an ultimate breaking strength of 1860 MPa. The 31 strand cable thus has a breaking strength of 8.6 MN, and the 67 strand cable 18.6 MN.

The stays are arranged in 4 fans, each having 18 cables, the shortest nearest to the tower are subjected to the lowest loads, whereas the flattest outermost cables have the highest loads. The cables outbalance each other horizontally at the tower anchorage, however minor deviations are acceptable, and forces may be slightly redistributed. Hence, the cables can be grouped and totally 6 different cable sizes are presented here.

The cable stays stressing ends are anchored in the steel boxes in the tower legs making the

tensioning process easy, whereas their passive ends are anchored at the bottom end of steel tubes sticking trough the verges of the bridge deck.

The cable sizes are determined by the maximum ULS load that may occur. ULS1 (permanent load dominant), the ULS2 (traffic load dominant) and ULS3 (wind/wave dominant) lead almost to the same loads, whereas ship collision not becomes critical. All load effects are comparable with those of other cable stayed bridges, except wave load effects to the longest stays nearest to axis 3. In

appendix I also the cable capacity for fatigue is checked and found to be very high. The main contributors to fatigue are traffic and tide. Traffic contributes most to fatigue near the tower while

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The load effects in each cable are tabulated in the stay cable drawing. Further documentation is enclosed in section 3.5.

The longest stays will require a damping system to be installed as also indicated on the drawings.

Additional damping might be necessary for the longest stays if snow is expected to accumulate on the stays. For reference, the Øresund Bridge has additional damping installed safeguarding against stay oscillations due to possible snow accumulation. The above topic is well known by the Joint Venture.

The stays constitute an important part of the cable stayed bridge, however, they are well-

documented standard products that are not supposed to add a significant risk to the project. The total quantity is 1000 tonnes approximately and constitutes about 15 % of the total cable stayed bridge cost. The construction is standard strand-by-strand installation.

1.7 Side span piers

The concrete piers are rectangular, 10–11 m wide and 2.0–2.5 m thick. The pier foundations are also rectangular with the below shown sizes all buried into the ground. The height varies in accordance with the terrain, and the tallest pier is about 56 m. The piers will be governed by the ship collision effects (ALS) and forces from the load combination ULS3. For the longest pier 1-E the load situation with wind on free standing pier is slightly governing for the foundation size and the reinforcement in the bottom of the pier. Since the heights are much shorter for the other piers (1-D is approximately 42 m high), the construction stages seem not to be governing for them.

The pier foundations will be cast directly on rock or blasted rock with a concrete scaling. All the foundations are placed above water but buried into the ground due to esthetical reason. The piers can be cast e.g. with jump- or slip form.

The foundation sizes:

1-A, 1-B, 1-C WidthxDepthxHeight: 7x15x3 m 1-D WidthxDepthxHeight: 7x18x3 m 1-E WidthxDepthxHeight: 8x18x3 m

1.8 Ship collision

Ship collision is a governing load situation and an important factor for the cable stayed bridge design.

The K11 alternative in the previous phase had the bridge deck and tower disintegrated transversely, with the purpose to distribute the elastic response as wide as possible. For this phase, a tight fit between bridge deck and tower has been selected. Thereby, the ship collision effect is more direct leading to high loads, but as the tower have such high strength, it becomes an appropriate design methodology.

The A-tower has a very robust lower frame that initially designed resisting a load of 50 MN, but actual load is found to be 35 MN. This force between the horizontal bearing on the side of the bridge deck and the inner side of the tower is slightly affected by the stiffness of the side-span piers.

The A-shape and wide distance between the tower leg foundations makes it very stable against ship collision, and the tower as such is far from being overloaded or overturned due to ship impact.

The strong axis bending moment of the bridge deck at the tower is 3300 MNm and is the most dominant ship collision effect. The effect to all the structures can more or less relate to this high moment. With the rigid approach, the south abutment is no longer subjected to severe moments as in the previous phase of the project.

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For ship collision to the pontoon axis 3 the bridge deck also experiences large bending moments at this end (and further into the floating bridge).

Torsion and shear effects are small, however, the shear between the tower and the nearest on-shore pier is high.

Ship collision is not critical for the stays and the tower legs above bridge deck.

1.9 Tidal variation of axis 3 support

The nearness of the axis 3 support subjected to vertical tidal movements has been a concern. The pontoon stiffness is however much higher than the cable stiffness, hence the cable stayed bridge will follow the deformations of the pontoon, basically.

However, the effect in terms of weak axis moments in the bridge deck, and additional cable loads for the outermost flattest cables, have shown to be only moderate. The cable forces will be rather immune for such design changes. This shows that the proposed system with 20 m between the no 18 stay anchorage and axis 3, and the inclination angle of 22⁰ seems a feasible and appropriate solution.

Even an extension of the distance between the outermost cable and the first pontoon support is not foreseen becoming a challenge. It has been evaluated to increase the distance by further 20 m without any notable impact to the design.

The outermost stay has furthermore been examined for fatigue due to tidal and wave motions showing sufficient capacity, please refer to Appendix I.

1.10 Construction

The construction of the cable stayed bridge contain working processes that are well known and straight forward. The bridge is situated on-shore except that a temporary bridge or embankment fill is required to provide access to Svarvahelleholmen. Due to limited space on the island, probably floating barges around the tower foot will be required for concrete works.

The works start with access roads and ground works for the south abutment, tower foundation and side span piers, with access roads between these sites. After preparation of the ground, the

foundations can be casted. Jump formwork is then used for construction of the lower tower legs and piers. Temporary strutting between the tower legs is required due to their inclination.

After completion of piers, span-by-span construction of the concrete side spans can begin. An overhung or underhung moving scaffolding system can be used, and the scaffolding system is shifted along the bridge span by span, with in situ concrete works. The bridge deck is cast monolithic to the pier tops (no bearings). The bridge structure is longitudinally post-tensioned as necessary for the construction stage. Full tensioning can await completion of the concrete works.

To reduce thermal constraint, it may be necessary to cast the stich joint connection to the abutment at a late stage after creep and shrinkage effects, and at neutral temperature.

The tower cross beam is cast in-situ supported by temporary scaffolding (truss) spanning between the legs. Hereafter the tower legs are cast by climbing formwork, alternatively by slip forming. Steel

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between the Svarvahelleholmen and Reksteren allows the side-span segments to be lifted off the barges also to this side, i.e. no steel element need to be transported on the ground.

When a steel segment has been lifted by the derrick crane and the joint is partly welded, the stays are installed. The cable is formed by individual strands that are pulled from the top and anchored at the bottom. When the stays are complete, and the steel segment joint is welded, the derrick crane can be moved further out ready for the next section. The segment installation continues until the segment towards the concrete spans is in place. The joint will be with in-situ stich concrete or grout, followed by tensioning of the longitudinal cables and bolts going through the joint.

The cycle of erecting steel segments is estimated to be in the range of 10-14 calendar days. It can however be done in parallel both sides for the first 2*7 segments.

The above erection schedule implies that the cable stayed bridge shall stay the winter fully erected without connection to the floating bridge. This situation is analysed and found not to be critical.

The bridge finishing works, pavement, barriers, bearings etc. are finally installed. A more detailed description of the different construction steps is given in appendix N Construction and marine operations.

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2 Abutments

2.1 General arrangement

The bridge is without expansion joints, and the bridge girder is fixed to the abutments both in south and north. This solution induces large forces to the abutments, and especially in north where the abutment was found to need about 2000 m² area, 52 m x 38 m, and a height of about 10 m to contain the necessary amount of ballast to achieve a weight of 60.000 ton. The weight/area is based on stability by weight only and a coefficient of friction 1.0 for concrete poured on cleaned rock surface.

In north the steel girder for the floating bridge is widened from 27 m to 36 m to suit the abutment, and large prestressing tendons are used in the steel/concrete connection.

In south the concrete approach bridge continues as the upper part of the abutment and is casted monolithically to the walls.

2.2 Analyses

The governing loading on the abutments is bending moment about the vertical axis, coming from environmental loads or ship impact. Below is summarised the max/min loading N is axial load in the bridge, positive sign is tension. Mz moment about the vertical axis, and My moment about the horizontal axis, positive sign is tension upper face. Units MN and MNm.

Table 2-1 Abutment north and south – design loads for ULS and ship collision Nmax Nmin Mzmax Mzmin Mymax Mymin

Ship imp. north 74 -77 5876 -5838 341 152

ULS 3 north 63 -55 2439 -2680 1196 -370

Ship imp. south 74 -75 606 -770 17 -15

ULS 3 south 69 -83 24 -24 128 71

Torsional moment and shear forces are not shown as they have a minor influence on the design.

2.3 North abutment

At the north abutment the road level is at elevation 11.6 m, and the area is chosen such that the entire abutment is above the water level. Ship impact governs the size of the abutment. With an abutment size of 50 m x 36 m, footprint 52 m x 38 m, the necessary height with iron ore ballast is around 10.0 m. Rock anchors can decrease the area or height but is not used at this stage.

A reduction of the ship impact forces will reduce the footprint/height, or olivine/gravel can be used as ballast instead.

The abutment is a large box structure with longitudinal walls lining up with the longitudinal bulkheads in the steel floating bridge. 150 nos. longitudinal prestressing tendons secure the connection to the bridge.

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Appendix L – Design of cable stayed bridge and abutments – K12 2 Abutments

Figure 2-1 North abutment - horizontal section

Figure 2-2 North abutment - transverse section

The position of the abutment can be shifted somewhat towards south and a shortening of the floating bridge can be achieved. Also, the fill concrete shown to the left can be avoided.

Below is shown an illustration of the northern part of the floating bridge ending at the north abutment and the transition into the tunnel.

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Figure 2-3 Illustration of the northern part of the floating bridge, abutment and tunnel entrance

2.4 Bridge deck joint

For the north abutment the strong axis bending moment is very high. The joint shall transfer these high moments, combined with other load effects, for example axial tension. The solution is to prestress the joint by large cables with a force large enough to avoid tension in the joint in the SLS limit state. Standard cables for bridges and offshore will be used. It appears that the SLS limit state is governing for the number/size of cables. These cables shall be grouted, alternatively unbonded with the possibility of later replacement.

It is proposed to place one cable inside between each longitudinal stiffener in the steel girder, i.e.

distance between 600 mm, all around the perimeter and along the webs. That means a total number of 150 cables are installed. A typical cable will have a breaking load of 5300 kN, (19 strands).

The steel box girder will end in a special cross frame, transition module, where the forces from the cables can be transferred to the longitudinal plates/stiffeners in the steel girder.

2.5 Approach bridge

Continuation north of the north abutment via an approach bridge has not been dealt with in this phase of the project.

2.6 South abutment

The south abutment needs a length of 30 m with a width equal the bridge width of 28 m. 9.5 m height is chosen as it fits well with the terrain and gravel ballast can be used. On this side the abutment is connected to a concrete bridge to which it will have a monolithic connection.

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Appendix L – Design of cable stayed bridge and abutments – K12 2 Abutments

Figure 2-4 South abutment - horizontal section

Figure 2-5 South abutment - transverse section

2.7 Ship collision

The ship collision is a very demanding load effect for the north abutment. The collision to the floating bridge leads to high strong axis bending moments, for which the gravity structure and connection shall be designed. The ship collision loads have varied throughout the project period and more refined analyses now show a strong bending moment of 5900 MNm. The fixity of the bridge

enhances the bending moments compared with those of the floating bridge in general. The widening of the bridge deck over some length near the abutment leads to sufficient increase in capacity, however, the increased stiffness will again give increased bending moments.

Introduction of a Vessel Traffic Management System in the area is being considered which probably will result in less forces from ship impact.

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2.8 Construction

Both abutments shall be built at solid rock, and it is expected to find it right below the ground surface. All work will be above water. In south about 2500 m³ rock shall be blasted for levelling off the bottom slab, and the double volume in north. A minimum 1 m thick bottom slab will be casted directly on rock forming the base for the abutment. The construction work should be quite

straightforward, but there are large areas, 7000 m² and 14000 m² formwork in south and north respectively and concrete volumes of 4000 m³ and 9000 m³. Both abutments shall be filled with solid ballast, in south 4000 m³ gravel and in north 11000 m³ iron ore.

In south the concrete bridge side span will be cast monolithically to the abutment. In north the floating bridge steel girder shall be attached to the abutment by 150 nos. prestressing tendons. The ducts will be placed in the walls and slabs in the abutment, and the structures casted until about 1.0 m from the position for the steel bridge. When the steel girder is in position the gap will be cast and the strands installed for anchorage in the steel bridge. The tendons will be stressed from the north side of the abutment.

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Appendix L – Design of cable stayed bridge and abutments – K12 3 Cable stayed bridge calculations

3 Cable stayed bridge calculations

3.1 Introduction

The analyses that support the cable stayed bridge (and abutment) design are combinations from different analyses:

• Global, dynamic wind and wave analyses of floating bridge (ORCAFLEX)

• Global dynamic analyses of ship collision to floating bridge (LS-DYNA)

• Permanent load, wind and traffic (RM Bridge)

• A local dynamic wind analysis of critical construction stages for the cable stayed bridge (Novaframe)

• Local cable stayed bridge (SOFISTIK) used for verification

The design checks for permanent stage for the different structural elements are based on forces from the global analysis. These analyses are documented in separate Appendices, primarily F, G and J. The load combinations used are envelope based. For dynamic loads such as dynamic wind and waves, separate time history analyses are done for wind and waves for a one hour storm (one seed).

The time history of the results, e.g. section forces, are then added linearly, and the maximum section force/moment combined with the other five coexisting section forces/moments at the time step is defining the envelope. This methodology is accurate enough to justify the technical feasibility and estimate the quantities.

The structural design capacities are checked for the following design forces:

 ULS forces during service: Maximum concurrent time history forces and moments from environmental load realisations load combined with static loads. In ULS2 traffic load is the dominating variable load combined with 1 year return period environmental loads. In ULS3 100 year return period environmental loads are the dominating variable load (“ULS2_ULS3” in capacity diagrams).

 ALS Ship collision: Maximum concurrent time history forces and moments from the different ship impact simulations for deck house and pontoon impacts combined with permanent static loads (“ALS-ship-deckh_pont” in capacity diagrams)

 ULS constructions stages: Frequency domain wind results for constructions stages a, b and c load combined with permanent static loads. (“CS_abc” in capacity diagrams)

The designed cross sections are generally chosen as equal to those in the global analysis models.

In the subchapters below, the design of critical structural components and sections is outlined. For more detailed documentation of the design of concrete sections, refence is made Enclosure L1 for plots, detailed listings and comparative plots for different load actions and bridge concepts. The following six concrete sections are evaluated:

Table 3-1 FE-model, structural parts and concrete sections

No Structural part Section No. of sections

1 Lower tower legs Connection to foundation 2 (east and west) 2 Lower tower legs Connection to cross beam 2 (east and west) 3 Tower cross beam Connection to tower legs 2 (east and west) 4 Side piers Connection to foundation 5 (5 piers)

5 Girder concrete side span Mid spans 5 (between all side piers) 6 Girder concrete side span Supports 5 (at all side piers)

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The design verification of the steel box girder is done within the global FE-model itself by

postprocessing routines using the same principles as for the floating bridge. The design verification is done using two different cross section types H1 and H2 with different plate thicknesses of the skin plates. General stresses are reported at corner points of the box girder along the box girder with 10.0 m spacing. The design verification is carried out using the reduced width method within Eurocodes.

3.2 Tower

The tower design will be driven by wind loads on the free-standing tower during construction, ship collision forces and maximum ULS forces during service.

Wind along the bridge on the free standing tower in construction stage is governing for the reinforcement in lower parts of the tower. The normal force is low for the tower in this stage and therefore have a small contribution to the capacity. (Compression force to a certain extend increase the bending capacity)

The ship collision leads to a very high transversal force between the bridge deck and the tower legs.

Still, ULS demands and ship collision demands are almost equal.

For the tower legs from deck level and upwards, ULS loadings will be governing. For the dimensions of the tower leg, quite conventional, these loads will not be very critical to the leg sections.

The steel anchor boxes will be subjected to the splitting cable forces, and they shall provide a tie between the pair of cables. Shear connectors shall transfer horizontal forces not being in equilibrium to the concrete walls. Based on comparison with similar concepts of other cable stayed bridges, it is relatively easy to design these steel elements for the local loads that are determined by the size of the cables.

3.2.1 Tower design

Capacity diagrams for bending-axial interaction are plotted for three critical tower sections below. A more detailed documentation is given in Enclosure L1.

The capacity diagram for the leg sections shows that moment about transverse axis is most critical compared to the moment around longitudinal axis. The most critical load is wind on free standing tower in construction stage.

Minimum reinforcement for the tower is according to Eurocode simplified 1.2% of concrete area with the used concrete and reinforcement quality. The reinforcement amounts in the diagrams are lower or not much higher than the minimum reinforcement.

For the cross beam both wind in construction stage, ULS and loads from ship impact, ALS are governing. Moment about the horizontal axis is governing.

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Tower legs at foundation interface

Figure 3-1: Capacity diagrams. Tower legs at foundation interface. Triangle – ULS2 & ULS3, red diamond – ALS ship collision, blue square – erection situations

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Tower legs at cross beam interface

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Tower cross beam at tower leg interface

Figure 3-3: Capacity diagrams. Tower cross beam at tower leg interface. Triangle – ULS2 & ULS3, red diamond – ALS ship collision, blue square – erection situations

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3.2.2 Tower foundation design

The foundation sizes are governed by wind forces on free standing tower during construction. The chosen sizes are 21x10x5.5. The height of 5.5 m is chosen so the horizontal reinforcement amounts in the cross section shall be moderate.

Following stability checks are performed for the critical load, wind during construction:

- Ground pressure is checked acc. to N400 11.2.3. Should be < 10MPa - Gliding is checked acc. to N400 11.2.5. Torsional moment is not considered - Overturning is checked acc. to N400 11.2.1

- Eccentricities also checked in SLS acc. to N400 11.2.2

The checks show a maximum ground pressure of 7 MPa in ULS to be the most critical check. For design checks in permanent stage ground pressure in ULS/ALS and indirectly overturning are checked.

The results show that in permanent stage, ship collision forces in ALS is more critical than the forces from ULS3 (wind and wave dominant) with a maximum ground pressure of 3.1 MPa, i.e. much lower than the ground pressure in construction stage.

Pressure less than 10 MPa on rock or on blasted rock are in most cases acceptable.

More detailed documentation is given in Enclosure L2.

3.3 Bridge deck 3.3.1 Bridge deck – steel

Layout

In general, the below FE-analyses of the steel box girder are based on the geometrical properties stated in the following excel files:

 Cross section type H1 used for the global FE-analyses, refer excel file K12_07_designers_format, sheet "input H1"

 Cross section type H2 used for the global FE-analyses, refer excel file K12_07_designers_format, sheet "input H2"

The geometrical properties for the two cross section types H1 & H2 are shown in the below figures.

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Figure 3-5 Cross section type H1, input for global FE-analyses - refer K12_07_designers_format sheet "input H1"

Figure 3-6 Cross section type H1, input of weight and cross section properties for global FE-analyses - refer K12_07_designers_format sheet, "input H1"

From above can be seen that for box girder type H1 the cross section area of the longitudinal steel becomes 1.297 m²equal to 10.2 t/m. For the cable stayed bridge more transverse steel is required compared to the floating bridge as the diaphragms at the stay anchorages shall be stronger. The transverse steel is therefore estimated to 20% of the longitudinal steel becoming 2.0 t/m. Steel for stay anchorages, full plated diaphragm at the tower location and longitudinal diaphragms in line with the bearings in vicinity of the tower, steel noses each side of the deck girder and steel for the

transition to the concrete box girder is estimated all in all to be approximately 4 t/m for cross section H1 and the below mentioned H2.

Section K12_H1_rev02 Cable stayed bridge section H1 - consept K12 Revision date: 05-06-2019 @ 12:30

K12_H1_02 Last revised by:

Bredde 27 [m] fra innside plate 3 til innside plate 5 Total bredde 27.037

Høyde 3.5 [m] fra OK plate 1 til OK plate 4 Total høyde 3.512

Plate 1 Plate 2 Plate 3 Plate 4 Plate 5 Plate 6

Thickness [mm] 12 12 25 16 12 12

La [m] 6.150 5.500 - 11.650 - 5.500

Lb [m] 9.850 1.540 - 15.350 - 1.540

L [m] 16.000 5.712 1.595 13.268 1.484 5.712

Trapzoidal type K12_H1-B K12_H1-IB K12_H1-VW K12_H1-T K12_H1-VW K12_H1-IB

Trapezoidal thickness [mm] 6 6 10 8 10 6

Trapezoidal c/c [m] 0.750 0.750 Kun én stiver 0.600 Kun én stiver 0.750

Bulb type K12_H1-B_b

Width h [mm] 280

Thickness t [mm] 11

Bulb radius r [mm] 12

Bulb height c [mm] 40

Bulb width [mm] 42

Bulb c/c [m] 0.6

Tverrsnittsdata, kassetverrsnitt:

Areal: 1.297 m2

Tyngdepunkt, fra OK: 1.463 m

Tyngdepunkt, fra UK: 2.049 m

Torsjonsmotstand*: 6.629 m4

Skjærareal vertikalt*: 0.0232 m2

Skjærareal transvers*: 0.7109 m2

2. Arealmoment, svak akse*** 2.534 m4

2. Arealmoment, svak akse**** 2.534 m4

2. Arealmoment, svak akse* 2.534 m4

2. Arealmoment, sterk akse* 89.531 m4

Treghetsmoment** 1348.672 tm2/m

Masse Areal: 10.18 t/m

Masse tverrrstål: 2.00 t/m

Sum stål: 12.18 t/m

Masse rekkverk: 0.71 t/m

Masse asfalt: 4.62 t/m

Sum masse: 17.52 t/m

Contingency: 1.48 t/m

Masse brukt i analyse 19.00 t/m

*basert på fullt tverrsnitt inkl. stivere (IDEA CSS)

** inkl asfalt, rekkverk etc.

***basert på tverrsnitt redusert for shear lag i bruksgrense-/utmattingstilstand Bøyemotstander **** basert på tverrsnitt redusert for shear lag i bruddgrensetilstand

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Figure 3-7 Cross section type H2, input for global FE-analyses - refer K12_07_designers_format sheet "input H2"

Figure 3-8 Cross section type H2, input of weight and cross section properties for global FE-analyses - refer K12_07_designers_format sheet "input H2"

From above can be seen that for box girder type H2 the cross section area of the longitudinal steel becomes 1.797 m²equal to 14.1 t/m. For the cable stayed bridge more transverse steel is required compared to the floating bridge as the diaphragms at the stay anchorages shall be stronger. The transverse steel is maintained at 2.0 t/m. Remaining steel for anchorages, wind noses etc, please refer to cross section type H1.

Section types

Tverrsnittsdata, kassetverrsnitt:

Areal: 1.797 m2

Tyngdepunkt, fra OK: 1.633 m

Tyngdepunkt, fra UK: 1.887 m

Torsjonsmotstand*: 9.663 m4

Skjærareal vertikalt*: 0.0342 m2

Skjærareal transvers*: 1.0057 m2

2. Arealmoment, svak akse*** 3.640 m4

2. Arealmoment, svak akse**** 3.640 m4

2. Arealmoment, svak akse* 3.694 m4

2. Arealmoment, sterk akse* 123.340 m4

Treghetsmoment** 1343.222 tm2/m

Masse Areal: 14.10 t/m

Masse tverrrstål: 2.00 t/m

Sum stål: 16.10 t/m

Masse rekkverk: 0.71 t/m

Masse asfalt: 4.62 t/m

Sum masse: 21.44 t/m

Contingency: -2.44 t/m

Masse brukt i analyse 19.00 t/m

*basert på fullt tverrsnitt inkl. stivere (IDEA CSS)

** inkl asfalt, rekkverk etc.

***basert på tverrsnitt redusert for shear lag i bruksgrense-/utmattingstilstand Bøyemotstander **** basert på tverrsnitt redusert for shear lag i bruddgrensetilstand

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Figure 3-9 Section types used in global FE-analyse - ,

The chainage for the different section types of the steel girder utilised in the global FE-model can be seen below and are found in the document K12_07_designers_format. For the cable stayed bridge cross section type H1 and H2 is utilised as follows:

Cable stayed bridge, side span: H1, chainage 38795 – 38850, length 55.0 m

H2, chainage 38850 – 38930, length 80.0 m

Cable stayed bridge, main span: H2, chainage 38930 – 39040, length 110.0 m

From above, the total length of steel box girder for the cable stayed bridge becomes 495 m. Please note that there can be small variation from above input into the global FE-models and the outcome shown on the drawings.

Design assumptions and verification

In the global FE-model stresses are taken out in corner points of the box girder, refer Figure 3-4.

The design verification is done within the global model by postprocessing routines using the same principles as for the floating bridge. In this section a summary will be presented showing important section forces, von Mises stresses and for the ULS design verification the reduced width method has been used in accordance with Eurocode, referred to as "method 2". Design verification will be done for the ULS design situations as well as the ALS design situations (ship collision).

Design verification of ULS2 & ULS3 load situations

The below figures have been taken from SBJ-33-C5-AMC-90-RE-107_0 Appendix G Global Analyses – Response as well as the results from K12_07_PROD_load_combinations_direct, dated 25. June 2019.

For the ULS load situations, the material factor is γm =1.1, which for steel S420 with mostly thin plates gives fyd = 420/1.1 = 382 MPa. This value has been used as the limit in the von Mises plots shown for the ULS2 (traffic load dominant) and ULS3 load situations (environmental load dominant).

The below 6 figures present and overview/envelopes of the section forces for ULS2 and ULS3 load situations. The steel deck of the cable stayed bridge is located within position A1 to A3.

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Figure 3-10 Bridge girder axial force – ULS. Note the additional compression force within the cable stayed bridge due to its nature

Figure 3-11 Bridge girder bending moment about strong axis – ULS

From the above figure is seen that maximum bending moment round strong axis becomes max/min 2100 MNm for the ULS3 load situations and only 1100 MNm for the ULS2 load situations. It is

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Figure 3-12 Bridge girder bending moment about weak axis – ULS

Figure 3-13 Bridge girder torsional moment – ULS

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Figure 3-14 Bridge girder vertical shear force – ULS

Figure 3-15 Bridge girder transverse shear force – ULS

In the below 3 figures a summary is presented of the max von Mises stresses obtained for load situations ULS2 and ULS3. For the cable stayed bridge it can been seen that in general the ULS3 load situations (environmental load dominant) is more severe than the ULS2 (traffic load dominant).

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Figure 3-16 Max von Mises stress for ULS2 and ULS3 in all stress points

Figure 3-17 Max von Mises stress for ULS2 in stress points

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Figure 3-18 Max von Mises stress for ULS3 in stress points

The 3 figures below present the design verification of the cable stayed bridge deck within the ULS load situations. In general, it is seen that ULS3 load situations govern the design and the utilisation ratio is below 1.0 unless 3 small peaks – one at the tower locations, another at the intersection between cross section type H1/H2 and the third when approaching the first pontoon of the floating bridge. All peaks of over utilisation are small and found acceptable at this level of design. Steel from other locations can be moved to these areas bringing the utilisation under 1.0 without increasing the total steel deck quantity.

Figure 3-19 Utilisation envelopes using capacity check "method 2" – ULS2 (blue), ULS3 (green)

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Figure 3-20 ULS2 - utilisation envelopes using capacity check "method 2"

Figure 3-21 ULS3 - utilisation envelopes using capacity check "method 2"

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Design verification of ALS ship collision

The below figures have been taken from SBJ-33-C5-AMC-27-RE-110_0 Appendix J Ship collision and ShipCollision_K12_06_revised, dated 26 June 2019, where the section forces are presented for ship collision towards the pontoons and deck house collision towards the box girder. For the cable stayed bridge, the overall dominant section force is the transverse shear force and the bending moment round strong axis as presented below.

For the ALS the material factor γm =1.0. Steel S420 with mostly thin plates gives fyd = 420 MPa.

The below 4 figures present shear force and bending moment round strong axis for all ship collision analyses carried out for "collision towards pontoon" and "collision towards bridge girder". The steel deck of the cable stayed bridge is located within position A1-E to A3.

Figure 3-22 Ship collision towards pontoon - shear force strong axis for all analyses

Figure 3-23 Ship collision towards pontoon – bending moment round strong axis for all analyses

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Figure 3-24 Ship collision towards bridge girder – shear force strong axis for all analyses

Figure 3-25 Ship collision towards bridge girder – bending moment round strong axis for all analyses To present a design verification of all the above analyses carried out becomes too comprehensive here and therefore a summary will be presented in the 5 figures presented below where all results are envelopes and summaries of the ship collision analyses carried out.

Figure 3-26 Axial force envelopes for the bridge girder, note the additional compression force within the cable stayed bridge due to its nature

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Figure 3-27 Strong-axis shear force envelopes for the bridge girder

Figure 3-28 Strong-axis bending moment envelopes for the bridge girder

From the above figure can be seen that deck house collision in general is worse that the pontoon collision, which is also applicable for the cable stayed bridge. The maximum bending moment round strong axis becomes 3300 MNm for deck house collision and 2800 MNm for pontoon collision.

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Figure 3-30 Envelopes of von Mises stress for the K12_06 bridge. Lines represent stresses, dots show the simulated impact locations

The envelope of von mises stresses in the bridge girder are shown in Figure 3-30. The response is almost within the elastic range for the cable stayed bridge, see A1-E to A3 which is judged to fully acceptable for the design verification of the ALS load situations at this stage of the project. Please furthermore note that a full design verification using the reduced width method has not

implemented for the ALS design situations. However, based on results from the ULS analyses, it can be expected that the utilisation will increase by approximately 10% when considering the full design verification using reduced width method (method 2). For the ALS ship collision this over utilisation is however found acceptable at this stage of the design.

3.3.2 Bridge deck – concrete

Capacity diagrams for bending-axial interaction are plotted for design forces at the side span support axes below. The reinforcement and prestressing amounts are chosen so that capacities are fulfilled for the different sections and load situations. It is possible, without getting any high reinforcement amounts or congestion problems, to increase the capacity considerably. More detailed

documentation is given in enclosure L1.

The capacity diagram for the section shows that moment about strong axis is most critical compared to the moment about weak axis. The most critical load is ship impact in ALS.

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Preferred solution, K12 – Appendix L Design of cable stayed bridge and abutments

Preferred solution, K12 – Appendix L Design of cable stayed bridge and abutments

SBJ-33-C5-AMC-22-RE-112

0

244

CONCEPT DEVELOPMENT, FLOATING BRIDGE E39 BJØRNAFJORDEN

Preferred solution, K12

Appendix L – Design of cable stayed bridge and abutments

TABLE OF CONTENTS

1 Cable stayed bridge

2 Abutments

3 Cable stayed bridge calculations